Servo mechanism



March 1950 CARL-GUSTAF HARD AF SEGERSTAD 2,500,407

SERVO-MECHANISM Filed Feb. 28, 1947 2 Sheets-Sheet 1 March 1950 cARL-GusTAF HARD AF SEG'ERSTAD 2,500,407

SERVO -ME CHANISM Filed Feb. 28, 1947 I 2 Sheets-Sheet 2 Patentecl Mar. Me, 1956 its at Claims.

The present invention relates to'servo-mechanisms or servo-motor units, that is, apparatus of the general type-comprising 'a fluid pressure operated motor and a valve device for controlling the supply of mild pressure to said motor in response to movements of anactuator. member.

An object of the-invention is to provide a servo-mechanism:which; While possessing a high degree of sensitivity and operating with a high degree of precision, isstill' of simple and compact'construction witha minimum of movable parts.

A'further object ofttheinvention is to provide an improved servo-mechanism of the type in which a valve member controlling the supply of fluid pressure to the motor is operated through a pressure difierence provided by a system comprising fluid flow control means operated by the actuator member of'the servonzechanism.

Other objects and advantages will be apparent to those skilled in the art from the following description of an embodiment 'ofthe invention illustratecl in the accompanying drawings, in which Fig. 1 is an elevation ofa servo-motor unit according to the invention, partly in section,

2 is an enlarged View, partly in section, of i the parts shown in the-upper right-hand corner of 1, viz; the valve unit and the ac-- tuatingmeans therefor,- and 3 is view of'the valve unit taken on the line--HIIII of Fig. 2.

The main parts of the servo-mechanism shown in l are an actuating device 1!, a valve unit 2 and a servo-motor 3, all of which parts are 35.

supported by aframe or housing t. The-valveunit is connectedpnone to an oilpump 1? through pressure conduit it, on the other hand to the servo-motor 3 through flexible-conduits 3 5,

body creasing securedwtothe housing Q-by of screws t a-pd provided with a through here '5 both ends 'of which are closed by threaded plugs t, 3, each of which is provided with a narrow central orifice :23;- E i, respectively: The

has slideably fitted therein a tubular -floating valve member illcooperating" with an. annular 5. et port it connectedaito.thepressuraconduit l i and a .pair of annular: outlet .ports" 5; l5 con-.-

nected .toncrificesrinot shown) in1the casing Dere 5G duitsuefi, 35, respectively; The piston rod ltis Referrin nowto Fig. 2. the valve unit has a cesses and cooperating with theoutlet ports M, It, respectively. The-recesses 32,33 are con.-.

nested-to the conduits.:34,.35 through bores 59,.8ll,..

respectively.

The ends of the tubularwvalvemember-mare. closed by threaded stoppers H, lZhaVingeaCh. a narrow central orifice 2|, 22, respectively. The

cavity enclosedbetween said. stoppers communicates with-the inlet port ISthrough radialholes idextending throughzthe collar 55.. The space.

enclosed betweenthe plug 8 and theleft eX- tremity of the valve member lflwith stopper ll constitutes a pressure chamber lathe inlet and. outlet of which areformed by the orifices 2t, 23;.

respectively, while the space enclosed. between the-ri ht extremity of the-valve member liiwith stopper it constitutes asecond pressure chamber. Zil, the inlet and outlet-ofuwhich. are formed by. Compression. springs 5 tend to .maintainthe valve member.

the orifices 22,. 24, respectively.

Hi in the normal positionshown. The escapeof fluid through. the outlets. 23,241 iscontrolled by a pair of checking-membersformed by screws 25, 28 :supportedby ayoke 27.1 The yoke is movably supported. by a. pair of. plate springs 28, 29 suspended in standards 3! 3! attached to the body or casing 5..

Theyoke 27 is adapted to be actuated through actuator bar Si by a diaphragm $3 mounted in a casing 54 one side of which may beconnected to a pressure system bymeans of the pipe socket 52, whereby the pressure variations of said sys-. tem tend to produce corresponding displacements of the. actuator bar. 6! and the yoke 21. The diaphragm 53 is biased by a spring 36 compressed between the diaphragm 28 and one arm of a lever 3'5 the other arm of which engages a set screw 38 having a head 3% by means of which the unit may. be adjusted to the normalworkihg pressure of the system connectedto pipe socket. 62..

The servo-motorll .(Fig. 1) comprises a cylinder cc pivotable about an. axle M, and a piston 42 with..piston.rod-. i3.. The .fluidchambers above and below the piston-are connected tothe conjointed to a lever 44 attached to an axle 45 iournalled in the frame or housing 4 and supporting outside of said housing an operating lever 48. Furthermore, said axle has attached thereto a cam disc 6? operating a crank-shaped slide lever 58 supported by the fixed axle 49. The lever i8 is provided with a pin 5| engaging a bail lever 59 connected to the yoke 21 through a spring 52, said spring being extended between one arm of bail lever 58 and a bracket 53 attached to the yoke 21.

The operation of the mechanism described shall now be explained. It is assumed that all parts are originally at rest and have the positions shown in the drawing. If now the pressure in the system connected to pipe socket 62 is raised by a small amount, the diaphragm 63 together with actuator 6i and yoke 27 will be dis placed towards the left, overcoming the resistance of spring 35. Said displacement produces a change of the ositions of the checking members 25 and 26 with regard to the respective orifices controled by said members, in such manner that the flow of fluid through the orifice 2 will be sub ected to an increased restrict on, whi e the flow of fluid through orifice 23 wi l be subjected to a decreased restriction, resulting in an increase of the pressure in the chamber 20 and a decrease of the pressure in the chamber 1?). The valve member ill will thus be displaced towards the left through the action of the resulting unbalanced pressure and cause fluid. pressrre to be applied to the lower side of the piston t2 through conduit 35. The piston is forced upwards. turning axle d5, cam disc 41 and operating lever 46 counter-clockwise. The cam disc l! forces the long arm of the s ide lever 58 outwards, causing said lever and the bail lever 58 to perform a counterclockwise rotation and thus to stretch the spring 52, so that said s ring will exert an additional pull upon the yoke 21, whereby the yoke is gradually restored to its normal position, in which the pressures in the chambers I9, 29 are balanced. As soon as this condition is reached, valve member ID will be returned to its .1;

normal position through the action of the compression springs 5Q. 55. lhe piston 42 and the various parts operated thereby will thus come to rest in a new position determined by the pressure acting upon the diaphragm 28.

The positive relationship between the angular position of the operating lever 46 and the pressure acting upon diaphragm 63 established by the spring 52 in connexion with the transmission members 57, $8 and 50 is generally desirable, for reasons well-known to anyone skilled in the art. Itshould be understood, however, that the invention is not limited to servo-mechanisms exhibiting such relationship.

What I claim is:

1. A servo-mechanism comprising, in combination, a casing, a bore in said casing, a floating valve member movable in said bore, a pair of closing members at either end of the bore, a chamber enclosed between one closing member and the adjacent end of the valve member, another chamber enclosed between the other closing member and the adjacent end of the valve member, means including a restricted passage for connecting each chamber to a source of fluid pressure, an outlet orifice for each chamber, fluid flow control means including a pair of movable checking elements adapted each to cooperate with one of said outlet orifices so as to control the fiow of fluid therethrough and an oblong frame member supporting both of the checking elements aforesaid and being itself supported at each end by at least one flat spring allowing of parallel frictionless motion of said frame member, said flow control means being so arranged that any movement thereof causing an additional restriction of the flow of fluid through one outlet orifice will at the same time cause a decrease of the restriction of the fluid flow through the other orifice, means for actuating said flow control means, and pressure fluid operated motor means adapted to be controlled by the valve member aforesaid.

2. A servo-mechanism according to claim 1, characterized in that the outlet orifices are provided in the closing members aforesaid.

3. A servo-mechanism according to claim 1. characterized by means including a yieldable member for connecting the fluid flow control means to the motor means.

i. A servo-mechanism comprising, in combination, a casing, a pressure fluid inlet port in the wall of said here, a floating valve member movable in said bore, a pair of closing members at either end of the bore, a chamber enclosed between one closing member and the adjacent end of the valve member, another chamber enclosed between the other closing member and the adjacent end of the valve member, a longitudinal conduit in said valve member communicating with each of said chambers through a narrow orifice and also communicating with the pressure fluid inlet port through at least one radial hole in the valve member, an outlet orifice in the wall of each. chamber, fluid flow control means including a pair of movable checking elements each adapted to cooperate with one of said orifices so as to control the flow of fluid therethrough, and an oblong frame member supporting both of the checking elements aforesaid and being itself supported at each end by at least one flat spring allowing of parallel frictionless motion of said frame member, said flow control means being so arranged that any movement thereof causing an additional restriction of the flow of fluid through one outet orifice will at the same time cause a decrease of the restriction of the fluid flow through the other orifice, means for actuating said flow control means, and pressure fluid operated motor means adapted to be controlled by the valve member aforesaid.

5. A servo-mechanism comprising, in combination, a casing, a bore in said casing, a floating valve member movable in said bore, a pair of closing members at either end of the bore, a chamber enclosed between one closing member and the adjacent end of the valve member, another chamber enclosed between the other clos ing member and the adjacent end of the valve member, means including a restricted passage for connecting each chamber to a source of fluid pressure, an outlet orifice for each chamber, fluid. flow control means including a pair of movable checking elements adapted each to cooperate with one of said out et orifices so as to control the flow of fluid therethrough, and an oblong frame member supporting both of the checking elements aforesaid and being itself supported at each end by at least one flat spring allowing of parallel frictionless motion of said frame memher, said flow control means being so arranged that any movement thereof causing an additional restriction of the fiow of fluid through one outlet orifice will at the same time cause a decrease of the restriction of the fluid flow through the other orifice, means for actuating said flow control means, pressure fluid operated motor means adapted to be controlled by the valve member aforesaid, a cam member adapted to be rotated by said motor means, a slide member engaging said cam member, and means including a spring for connecting said lever to the fluid flow control means aforesaid.

CARL-GUSTAF HARD AI SEGERSTAD.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Moore Apr. 1, 1941 Brown Nov. 4, 1941 FOREIGN PATENTS Country Date Great Britain Oct. 31, 1921 

